This invention relates to an ultrasonic welding apparatus. More particularly, this invention relates to a spot welding tip for an ultrasonic welding apparatus.
Ultrasonic welding has been used for bonding in a number of materials. Most commonly, ultrasonic bonding is utilized in thermoplastic materials. Recently, it has been discovered that ultrasonic spot welding could be accomplished. See, for example, the November-December, 1980 issue of Plastics Design Forum, page 86. This publication describes techniques of ultrasonic spot welding as well as the advantages in producing a clean appearance on the surface opposite the weld. This article describes a process for welding two thermoplastic sheets together wherein a standard welding tip penetrates one sheet and extends halfway through the second. The article further addresses the possibility of inverse spot welding, that is, fitting the welding tip to a mounting fixture or anvil, and utilizing a flat-faced horn to provide ultrasonic energy.
The use of ultrasonic spot welding is further described in an article entitled "Ultrasonic Assembly", by R. A. Clarke, published in the 1980-81 Modern Plastics Encyclopedia, pgs. 447-450. In this article, Clarke discloses the general advantages of an annular ring design in the horn or tip for ultrasonic spot welding.
None of the above-referenced ultrasonic welding tip configurations or methods provide a suitable means for permitting the free flow of melted thermoplastic material away from the weld joint and tip therein during the welding process. The accummulation of melted material in this region may interfere with the continued melting of the unmelted material at the weld joint (it absorbs ultrasonic energy) and so lends itself to thermal degradation which may result in a weld joint of insufficient strength. Furthermore, this melted material may cause overheating of the weld tip configuration, which can damage the welds and surrounding sheet material.